Human C5a anaphylatoxin is a low molecular weight glycopolypeptide released from the fifth component of complement during complement activation. It is a potent acute inflammatory mediator, serving to trigger a variety of granulocyte responses after it binds to specific cellular receptors. The major goals of my proposed investigations are two-fold. First, to conduct fundamental studies that are aimed at delineating the nature of C5a-receptor interactions. Second, to apply this information in an attempt to provide clinical diagnostic criteria of intravascular complement activation and altered granulocyte function. To accomplish this I specifically propose the following series of investigations. Murine monoclonal antibodies will be produced against purified human C5a and rabbit anti-human C5a. These reagents will facilitate large-scale purification of C5a and serve as ligand probes of the C5a receptor. The C5a receptor of human neutrophils and the P388D1 cell line will be purified and characterized. Structural analogs of C5a will be prepared by chemical and enzymatic methods. Studies that utilize well-defined C5a derivatives and purified receptor preparations should provide a clear understanding of the structural features of both the ligand and the receptor that regulate binding interactions. Controlled studies conducted in a rabbit animal model and with patients undergoing hemodialysis will permit measurements of complement activation, neutrophil deactivation, C5a receptor "down regulation" and cellular degranulation. It is anticipated that these four separate phenomena will be interrelated. Taken together, these measurements should provide both a clear understanding of the perturbations of granulocyte function that result from C5a formation in vivo and delineate clinically useful criteria for assessing human complement activation. Because the C5a-activated granulocyte appears to play a significant role in the pathogenesis of such diseases as adult respiratory distress syndrome and myocardial infarction, these types of studies offer the opportunity to not only develop therapeutic reagents predicated upon a knowledge of ligand-receptor interactions but also may permit early diagnosis of these types of diseases.